640 EDWARD T. BROWNE. 



not able to proceed any further. Next we have some very early 

 free-floating stages described by Lankester (PI. 35, tigs. 7 

 and 8). Although there is still no absolute proof that the 

 Medusa-buds found upon the Hydroid do develop into the 

 Medusa known as Limnocodium, still the circumstantial 

 evidence is very strong. 



I have seen many species of marine Hydroids bud off 

 Medusa3, but have never seen Medusae liberated at such an 

 early stage as those of Limnocodium^ which look as if they 

 were developing direct from eggs. On the other hand, the 

 Medusa of Microhydra looks like a Medusa which has just 

 been liberated from its Hydroid, and Mr. Potts states that 

 probably none of the specimens seen were more than two or 

 three days old. The Medusa of Microhydra on liberation 

 is at a far more advanced stage than the earliest floating 

 embryos of Limnocodium. (Compare PI. 35, fig. 8, with 

 PL 36, fig. 13). 



The embryo of Limnocodium has already got one sense 

 organ developed, so one would expect to find sense organs in 

 the Medusa of Microhydra if it had any. If an adult 

 Medusa has sense organs one always finds (I cannot remember 

 an exception) a certain number (generally about four or eight) 

 of sense organs present in the young Medusa when ready for 

 liberation. To pin one's faith on the absence of sense organs 

 in preserved specimens is not a safe proceeding, because 

 sensory vesicles have at times a wonderful way of becoming 

 invisible after preservation, especially when alcohol is used. 

 Their disappearance is generally due to excessive shrinkage 

 of the tissues when the specimens are too rapidly transferred 

 from sea water to strong alcohol. The great advantage of 

 dilute formalin is that it does not produce a shrinkage of the 

 jelly, and that the sense organs can be more easily found. 



The great difference between the Medusa of Microhydra 

 and that of Limnocodium lies in the structure of the 

 tentacles. A few years ago I found out that the shape and 

 structure of the tentacles, and particularly the shape of the 

 basal bulb, were an exceedingly useful and reliable aid in 



